Crosslinked carboxy-terminated polyether propellant compositions containing nitrato esters



United States Patent Ofi US. Cl. 14919 3 Claims ABSTRACT OF THE DISCLOSURE Carboxy-terminated polyethers having the general structural formula:

limp-E II M wherein R and R are hydrocarbyl groups containing 2-4 carbon atoms, k and n are integers whose sum is not less than 4 nor more than 60, m is an integer not less than 6 nor more than 70 and the value of the relationship k+n/k+m+n is not less than 0.2 nor more than 0.6. Such polymers are compatible with the nitrato esters used in high burning rate propellants, high density propellants and metal hydride containing propellants and can be crosslinked with a crosslinking agent having a functionality greater than 2 to produce nitrato ester plasticized propellants having good mechanical properties.

BACKGROUND OF THE INVENTION High burning rate and high density composite propellants incorporating high energy nitrato ester plasticizers have been prepared in which crosslinked carboxy-terminated polyesters are employed as the binder. These propellants have not been found to be completely satisfactory because the high plasticizer content detrimentally affects the mechanical properties of the propellant and the uncured propellant mix is too viscous to permit processing at the high solids loadings which are needed to obtain high impulse propellants. According to this invention a [ice novel class of prepolymers has been developed which exhibit excellent solvency for the nitrato ester plasticizers, have relatively low viscosities with high solids loadings and can be crosslinked to produce propellant compositions having good mechanical properties.

It is accordingly an object of this invention to provide a novel carboxy-terminated difunctional prepolymer.

It is another object of this invention to provide a prepolymer that is compatible with nitrato ester plasticizers.

It is another object of this invention to provide a high burning rate composite solid propellant plasticized with nitrato esters.

It is another object of this invention to provide a prepolymer having relatively low viscosity at high solids loadings.

It is another object of this invention to provide a nitrato ester plasticized composite solid propellant having good mechanical prperties.

These and other objects of this invention will be readily apparent from the following description of the invention.

DESCRIPTION OF THE INVENTION In accordance with the above objects useful prepolymers according to this invention are carboXy-terminated polyethers having the following structural formula:

ethylene groups do not exhibit good solvency for nitrato TABLE I esters. Also, the proportion of oxyethylene and oxypro- E W M 1 W G If pylene be selected as shown, since too great an oxyethyl- Sample k+n m f 3' f fii ene content raises the glass temperature to undesirable levels thereby detrimentally affecting physical properties 1 g? 33% 32 of a propellant at low temperatures, and too great an oxy- 5 1s 21 1: 229 2: 200 2. propylene content causes reduced solvency for the nitrato 26 30 1,386 ester plasticizer. The total molecular weight of the pre- Numfber average molecular weight determined by vapor phase S polymers accordmg to the abqve relatlollshlp ranges from 0 l l tlr he measured by Sunshine gel timer at 90 C. Formulation about 1000 to about 5400, yields materials having procconsists of tr is[1-(2-methylaziridinyb] phosphine oxide (MAPO) and essable viscosities and produces cured propellants with polymer; equivalence ratlo, azlridmelearboxyl==1.3/1.0. good mechanical properties. If the cured propellant is The polymers according to this invention can be cured desired to have high elongation, a high molecular weight with a variety of crosslinking agents having a functionality prepolymer is used and if high tensile strength is required greater than 2. A large number of suitable crosslinking the low molecular weight prepolymer is used. agents are known to the art and include, while not being The prepolymers according to this invention are readily limited to, MAPO; tris-(1-aziridinyl)-s-triazine; tris-(lsynthesized from commercially available materials. One aziridinyl)phosphine oxide; tris-(2-ethylaziridinylmethyl) basic approach is an acid-catalyzed esterification of a dicyrnel; tris-[1-(2-ethyl)aziridinyl]-s-triazine; tris-[1-(2- car'boxylic acid anhydride having from 4 to 6 carbon methyl)aziridinyl1-s-triazine; 2,2,2-nitrilotriethyl-fi-[1- atoms with a polyether having hydroxyl functionality of (2-methyl)aziridinyl]butyrate; 2,2',2"-nitrilotriethylfi-[1- 2.0 according to the following reaction: (Z-methyl)aziridinyl1propionate; tris-l,3,5-[1-(2-methyl) CH3 CH2-CH2 I I p-toluenesulfonie acid H(O C2Hl)k (OCH3C) -(O CzH4) nOH 2 0 O 0 CH3 0 HO- H CHz--OHz (0 C2H4)k(O CH2( 3)m-(O CzHi) nOAl-CH2-CHz( 3=OH The values of k, m and n in the hydroxy-terminated aziridinylpropionyl]-hexahydro s triazine; tris-l (2- polyether will be the same as desired in the end product, methy1)aziridinyl phosphine sulfide; 1,2,3-tris-(2,3-epoxyand such polyethers are commercially available in almost propoxy) propane; 1,1,3-triS-[4-(2,3-epoxypropoxy h any desired combination yl) ]propane; N,N-bis- (2,3-epoxypropy1)-4-(2,3-epoxypro- Example 1 poxy)aniline; 1-(2,3-epoxypropoxy)-2,6-bis-(2,3-epoxy- O a HO-PJCH2-CHZI(IJ(O C2H4)k(0 OHZ m '(O C2H4) D-O(Q-CHZCH2(III7OH The following specific procedure is illustrative of the propyl)benzene and triglycidyl ether of 1,2,3-trimethylacid-catalyzed synthesis of the polymers of this invention. olpropane.

A hydroxy-terminated block polyether having the de- The polymers of this invention are extremely useful in sired arrangement of oxyethylene and oxypropylene the preparation of nitrato ester plasticized propellants. groups is employed as the starting material. In this case Suitable high energy nitrato esters are known to the art 290 gm. of Wyandott Pluronic L64 (eq. wt. 1450), 100 and include, while not being limited to, trimethylolethane gm. succinic anhydride, 3.9 gm. of p-toluenesulfonic acid trinitrate; triethyleneglycol dinitrate; 1,2,4-butanetriol triand 150 gm. of the anhydrous inert solvent, dioxane, were nitrate; 1,4-butanediol dinitrate; diethyleneglycol dinitrate; placed in a one liter, three-necked, round bottom flask pentaerythritol trinitrate; glycerol trinitrate and polyglyfitted with a stirrer, nitrogen gas inlet and a reflux concidyl nitrate. The polymers of this invention exhibit exdenser having a drying tube to exclude atmospheric cellent solvency for such nitrato esters and can be used moisture. A small flow of nitrogen was used to maintain to produce high energy binders which employ as high as an inert atmosphere during synthesis. The reactants were by weight of the ester. stirred and maintained at C. for four hours and then In addition to the nitrato esters, the propellants can transferred to a 500 ml. wide mouth Erlenmeyer flask contain solid inorganic oxidizing salts such as ammonium which was covered and allowed to cool to room temperaperchlorate, ammonium nitrate, alkali metal nitrates and ture. Unreacted succinic anhydride precipitated from soperchlorates; solid fuel materials such as metals, metal lution. Approximately 150 ml. of benzene was added to 5 y n, boron hy and ballistic modifiers the mixture and the precipitated anhydride was removed such as iron oxide, chromic oxide and ferrocene as is by filtration through a Buchner funnel. The filter cake known to the art. was washed with about 50 ml. of benzene and the filtrate Example 2 was Stripped P solveflt 700 m a rotary vacuum A carboxy-terminated polyether according to this ineliaporator- Fmal Punficatlon of the Product was accom' 70 vention having the formula of Example 1 with k-l-n equal phshed by removal of volatile constituents in a wiped to about 22 d m equal to about 16 and h i a molecfilm molecular still at a pressure of 0.02-0.03 torr and ular weight of about 1935 was compared with a prior awall temperature of C. art carboxy-terminated polyester having a molecular Properties of polymers produced according to this procweight of about 2000 from the standpoint of viscosity and ess are shown in Table 1. easy of processing. The viscosity was measured at 24 C.

The polymer of this invention exhibited a viscosity of 1900 c.p.s. whereas the polyester exhibited a viscosity of 22,400 c.p.s. It is readily apparent that the lower viscosity of the polymer according to this invention will result in greatly improved processing characteristics.

Example 3 Propellant grains weighing about 30 gm. were cast and cured in the form of internal burning cylinder 2 in length, 0.70" CD. and 0.3" ID. from the compositions of Samples 8 and 9.

Micromotor firings of these grains at various chamber pressures produced the results shown in Table II.

TAB LE II Average chamber Burning rate,

carboxy-terminated polyether block polymer having the structural formula:

CH 0 O a H m Composition of samplepressure (p.s.i.a.) in./sec.

540 44 wherein R and R are hydrocarbyl group having from 2 1, 050 0. 55 to 4 carbon atoms, k and n are integers whose sum is not '22? gless than 4 nor more than 60, m is an integer not less 1,000 0:53 than 6 nor more than 70 and the value of the relation- 2100 73 ship k+n/k+m+n is not less than 0.2 nor more than 0.6

having liquid nitrato ester dissolved therein. Example 4 Carboxy-terminated polyethers having the general structural formulas of Example 1 were formulated into propellants having the compositions and mechanical properties of Table III.

2. The composition of claim 1 further comprising a crosslinking agent for the compound of claim 1, said crosslinking agent having a functionality greater than 2.

3. The composition of claim 2 further comprising an inorganic oxidizing agent dispersed therethrough.

TABLE III Sample Ingredients 3 4 5 6 7 8 9 Carboxy-terminated polyether:

k+n 22 11 11 18 18 26 26 m 16 21 21 21 21 30 30 Eq. Wt A 961 1007 947 961 1229 1493 1576 Wt. percent. 9. 89 7. 01 6. 92 6. 94 7. 27 7. 51 7. 56 TBM: 1

Eq. w't 100 100 100 100 100 100 100 Wt. percent 1. 54 1. 04 1. 10 1. 08 0. 89 0. 0. 72 Epon 812: 2

Eq. wt 154 154 154 154 154 154 154 Wt. percent 1. 07 0. 75 0. 78 0. 78 0. 64 0. 54 O. 52 'IME'IN. 3 Wt. percent 12. 50 8. 80 8.80 8.80 8. 80 8. 80 8. 80 Aluminum, 40 micron: Wt. percent 21. 00 16. 00 16. 00 16. 00 16.00 16. 00 16. 00 Ammonium Perchlorate:

190 micron, wt. percent- 32. 40 46. 48 46.48 46.48 46. 48 46. 48 46.48 12 micron, wt. percent 21. 60 19. 92 19. 92 19. 92 19. 92 19. 92 19. 92 Mechanical properties at 77 F alter cure:

Stress, max. p.s.i 99 154 148 89 75 53 Elongation at max. stress percent- 29 22 15 19 27 41 53 l Tris (butylenimino)melamine. Z An aliphatic polyfunctional epoxide manufactured by shell Chemmal Company. 3 Trimethylolethane trinitrate. 4 Cured for 5 days at F.

References Cited UNITED STATES PATENTS 3,029,216 4/1962 Bailey et a1. 260-823 3,050,423 8/ 1962 Hudson 149-19 3,130,096 4/1964 Pruitt et al. 149-19 3,177,190 4/1965 Hsieh 260-942 3,278,352 10/1966 Erickson 149-19 3,305,523 2/1967 Burnside 260-465 3,344,003 9/1967 Miranda et al 149-19 BENJAMIN R. PADGETT, Primary Examiner US. Cl. X.R. 

